macOS: There is no connected camera

An odd thing happened to one of the office laptops the other day. It was a brand new machine with macOS Sierra installed. The initial install was just finished, and only a few apps (atom.io, Keka, MacVim, Propellerhead Reason) were installed. When the Photo Booth or FaceTime apps were opened, however, the camera light would not come on. Instead, the screen presented an error which read "There is no connected camera". After checking the system profiler, it was confirmed that macOS could actually see the camera and its model.

The installed applications were benign, and none of them utilized the camera, so it couldn't have been a result of those.

This scenario turns out to be the result of an application reserving the camera via VDCAssistant but not releasing it. There are two quick fixes to this.

The nuclear option is just to reboot the machine

Alternatively, you can kill the VDCAssistant process and it should automatically re-spawn, reclaiming the camera with it

To deal with VDCAssistant, you can simply open the terminal and type the following command:

$ sudo killall VDCAssistant

Once this was run, both Photo Booth and FaceTime could utilize the camera without errors.